Ammonia is an important industrial chemical that has many uses including (a) direct application to the soil as a fertilizer, (b) as a raw material for the manufacture of urea, which in turn has uses as a fertilizer and in the manufacture of plastics, and (c) as a raw material for the production of other chemicals such as nitric acid, ammonium nitrate, ammonium sulfate, ammonium phosphates and acrylonitrile.
Ammonia is manufactured industrially using the Haber-Bosch process, invented by Fritz Haber in 1905 and developed for industry by Carl Bosch in 1910. About 150 million metric tons of ammonia are produced globally every year based on this process. Data for ammonia production are available at https://minerals.usgs.gov/minerals/pubs/commodity/nitrogen/).
Processes for ammonia production are described in Ullmann's Encyclopedia of Industrial Chemistry, 7th ed (Wiley-VCH, DOI: 10.1002/14356007) and in Kirk-Othmer Encyclopedia of Chemical Technology. (Wiley, DOI: 10.1002/0471238961).
The primary reaction in the Haber-Bosch process is the high-pressure, catalytic reaction of nitrogen and hydrogen:N2+3H2→2NH3  (R1)
In general, the source of nitrogen is air whereas that of hydrogen is a hydrocarbonaceous material that has been converted to a hydrogen synthesis gas.
The hydrogen synthesis gas is conventionally generated by one of the following routes: (1) steam reforming of gaseous hydrocarbonaceous feedstocks such as natural gas and (2) noncatalytic gasification of solid hydrocarbonaceous feedstocks such as coal or petroleum coke with oxygen and steam.
When the hydrocarbonaceous feedstock is natural gas, the process of steam reforming is predominantly used to generate hydrogen synthesis gas, which is a mixture comprised of hydrogen, carbon monoxide, carbon dioxide and unreacted methane. In steam reforming, the natural gas is reacted with steam in the presence of a catalyst at a temperature of about 800° C. (1472° F.) via the reforming (R2) and water-gas shift (R3) reactions:CH4+H2O↔CO+3H2  (R2)CO+H2O↔CO2+H2  (R3)
The reforming reaction is highly endothermic and is carried out in a furnace known as the primary reformer that contains tubes of nickel oxide catalyst on an alumina support. The temperature is chosen to allow for about 7-15% of the methane in the feed to remain unconverted in the product from the primary reformer.
Air is then added to the product from the primary reformer to provide the nitrogen required for ammonia synthesis. The mixture is then passed over another catalyst bed known as the secondary reformer that contains a catalyst similar to that in the primary reformer. Within the secondary reformer, exothermic partial oxidation reactions proceed at a temperature of about 1000° C. (1832° F.) that reduce the methane content to about 0.5 mol % or less and drive the oxygen to extinction. Subsequently, a series of water-gas shift reactors are employed to convert the carbon monoxide to hydrogen using additional steam if necessary.
After subsequent removal of acid gases, carbon dioxide and hydrogen sulfide, the resulting gas is comprised of hydrogen and nitrogen with small quantities of carbon monoxide. Since the ammonia synthesis catalyst is poisoned by carbon oxides, a trim methanator is employed to convert the remaining carbon oxides to methane via reaction with hydrogen.CO+3H2↔CH4+H2O  (R4)CO2+4H2↔CH4+2H2O  (R5)
The stream leaving the methanator is an ammonia synthesis gas with an optimum molar ratio (R) of hydrogen to nitrogen in the range of 3 to 3.5.
It may be noted that the judicious choice of a low operating temperature of about 800° C. (1472° F.) in the primary reformer not only produces a gas with a high hydrogen to carbon monoxide ratio of about 6 but also allows a sufficiently high methane-slip that is converted with air in the secondary reformer to a hydrogen synthesis gas while simultaneously introducing nitrogen in the correct stoichiometric ratio for ammonia synthesis.
On the other hand, conventional noncatalytic gasification of coal and petroleum coke produces a synthesis gas with a low hydrogen to carbon monoxide ratio of 0.5 to 1.0 and virtually no methane. The high operating temperature (about 1427-1593° C. or 2600-2900° F.) results in high oxygen consumption. The large deficiency of hydrogen must be met by subjecting a significant fraction of the synthesis gas to the water-gas shift reaction (R3) in a series of water-gas shift reactors. Shifting the gas to increase the hydrogen content is undesirable since it lowers the effective carbon conversion to hydrogen. Further, all the gasification must occur with nearly pure oxygen to allow the high temperatures to be attained that maximize the conversion of the organic carbon content of the hydrocarbonaceous feedstock. Consequently, conventional noncatalytic gasification of solid hydrocarbonaceous feedstocks for ammonia production cannot be carried out with air as an oxidant. Further, under the high-temperature conditions of noncatalytic gasifier operation, methane cannot be formed. Hence, it is not possible to stage the oxygen between the noncatalytic gasifier and a partial oxidation reactor.